Not Applicable.
Not Applicable.
1. Field of the Invention
The present invention is directed generally to a transformer and, more particularly, to a transformer incorporating a telescoping bobbin.
2. Description of the Background
To meet the lawful safety standards issued in each country, a transformer must satisfy a host of safety standards regulated by various agencies in each of the countries. One important safety standard that relates to a transformer is what is commonly known as creeping insulation distance. The creeping distance may be defined as the shortest distance between adjacent conductors measured along the surface of a solid dielectric material interposed therebetween. If the creeping distance between such adjacent conductors is too short, a spark discharge may sometimes arise between the adjacent conductors. Where the insulation between the adjacent conductors is not sufficient, a spark discharge between adjacent conductors may occur.
Whenever high voltage is present, the various safety agencies dictate specific insulation requirements between adjacent conductors of the transformer to minimize the risk of injury to personnel working with or near the transformer. One example of a case where a high voltage is present is a low voltage power supply that is energized with a voltage from utility mains. Such a power supply typically includes a transformer with at least one primary winding electrically coupled to the utility mains. A secondary winding or windings may provide the low voltage outputs and voltages less than 40 Volts RMS are generally considered safe.
To help insure that the mains voltage is not inadvertently shorted to the low voltage windings through the insulation, it is known in the art to use multiple modes of electrical insulation between the windings. One method is to use two or three layers of thin insulating material to separate the primary and secondary windings, wherein each layer of electrical insulation has sufficient dielectric strength to withstand an elevated voltage. Another method is to place a single layer of sufficiently thick and solid insulation between the primary and secondary windings. Nevertheless, the layer or layers of insulation have boundaries or margins, and electrical paths connecting the primary winding to the secondary winding may form around these boundaries without passing directly through the insulation. As a result, the various safety agencies also require certain minimum spacing around any such boundaries (creeping distance) or through any air gaps (clearance) to minimize the potential of the formation of such electrical paths. It is known in the art to use spacers of insulating material such as margin tape to help meet these minimum spacing requirements. However, the required electrical spacings may approach the total length of the windings, leaving little or no space to place the windings. It is also known in the art to use tubular sleeving over the ends of the windings to increase the creeping distance around the boundaries. However, the use of margin tapes or sleeving limits the degree of winding automation that is possible.
A telescoping bobbin, also known as a concentric bobbin or coaxial bobbin, has been utilized to help eliminate the need to use margin tapes or sleeving to meet the required safety standards. The telescoping bobbin typically includes an inner bobbin that carries a primary winding and a separate outer bobbin that carries a secondary winding, where the thickness of the material comprising the inner and outer bobbin is sufficient to provide the required insulation in a single layer. The telescoping bobbin also typically includes flanges on each end of the inner and outer bobbins that extend the creeping distance between the primary and secondary windings. An example of such a telescoping bobbin is disclosed in U.S. Pat. No. 4,617,543.
As the size of transformers decrease, the ability to achieve the required spacings, becomes increasingly difficult. For the relatively small transformers required by certain applications, even transformers incorporating telescoping bobbins known in the art will not meet the required safety standards. Thus, there exists a need for a transformer that overcomes the limitations, shortcomings, and disadvantages of prior art transformers.
The present invention meets the identified need, as well as other needs, as will be more fully understood following a review of this specification and the accompanying drawings. The present invention is directed generally to a transformer that incorporates a telescoping bobbin to overcome isolation clearance problems associated with decreasing the size of prior art transformers. The telescoping bobbin of the present invention, according to one embodiment, includes a first bobbin element and a second bobbin element adapted to receive at least a portion of the first bobbin element. The first bobbin element includes a first member having first and second ends, a first flange extending from the first end of the first member, and a first base extending from the second end of the first member. The second bobbin element includes a second member having first and second ends, a second flange extending from the first end of the second member, and a second base extending from the second end of the second member. The second flange includes first and second portions. The first portion extends generally outward from the second member and the second portion extends generally inward from the second member. When the first bobbin element is received by the second bobbin element, the second portion is adjacent the first flange and the second base covers at least a portion of the first base.
According to another embodiment, the telescoping bobbin of the present invention includes a first bobbin element and a second bobbin element adapted to receive at least a portion of the first bobbin element. The first bobbin element includes a first member having first and second ends, a first collar extending from the first member proximate the first end of the first member, and a first flange extending from the second end of the first member. The second bobbin element includes a second member having first and second ends, a third collar extending from the second member proximate the first end of the second member, a second flange extending from the second end of the second member, and a fourth collar extending from the second member proximate the second end of the second member. The second member includes a shoulder extending therefrom proximate the first end of the second member and a neck portion at the first end of the second member. The fourth collar is between the third collar and the second flange.